The prostaglandins are widely distributed in the gastrointestinal tract, but the physiological role of these compounds is poorly understood. They have been shown to be remarkably cytoprotective in the stomach and small intestine, but the mechanism of this action is unknown. The objectives of this study are to characterize the effects of prostaglandins on the electrical characteristics, transport, and alkaline secretion of isolated frog fundic gastric mucosa inhibited with an H2-receptor antagonist, frog antrum and from duodenum in vitro. Previous studies indicate that prostaglandins stimulate chloride transport in isolated frog antrum and fundus and suggest that cytoprotection may be effected by facilitation of a Cl ion/HCO3 ions exchange. The present studies are designed to test that hypothesis and also to examine the effect of the prostaglandins is mediated via the cyclin AMP system. Specific inhibitors of PG synthetase and prostaglandins themselves as well as dibutyryl cyclic AMP and phosphodiesterase inhibitors will be tested. The effects of the latter compounds as well as various prostaglandins on Ca ion depleted tissues will be assessed.